Conventionally, a torque estimation apparatus that estimates magnitude of available torque that is usable in an engine of an aircraft has been known (for example, see Patent Literature 1). The torque estimation apparatus stores therein measurement points having measured values of a parameter related to performance of the engine in association with measured values of engine torque for those measured values, together with times of the measurement. The torque estimation apparatus generates, based on the stored plural measurement points, an approximate equation for a performance curve, and estimates an available torque from a performance curve of the generated approximate equation. If more than one measurement point is unable to be obtained, the approximate equation is unable to be generated, and thus a performance curve of an approximate equation that has been obtained beforehand is parallelly translated to a measurement point, and an available torque is estimated from the parallelly translated performance curve.